/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.coderside.fragment.arithmetic.packchars;

import java.io.ByteArrayOutputStream;

/**
 * Library of utility methods useful in dealing with converting byte arrays
 * to and from strings of hexadecimal digits.
 *
 * @author Craig R. McClanahan
 */

public final class HexUtils {
	// Code from Ajp11, from Apache's JServ

	/**
	 * Convert a String of hexadecimal digits into the corresponding
	 * byte array by encoding each two hexadecimal digits as a byte.
	 *
	 * @param digits Hexadecimal digits representation
	 *
	 * @exception IllegalArgumentException if an invalid hexadecimal digit
	 *  is found, or the input string contains an odd number of hexadecimal
	 *  digits
	 */
	public static byte[] convert(String digits) {

		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		for (int i = 0; i < digits.length(); i += 2) {
			char c1 = digits.charAt(i);
			if ((i + 1) >= digits.length())
				throw new IllegalArgumentException("Odd number of hexadecimal digits");
			char c2 = digits.charAt(i + 1);
			byte b = 0;
			if ((c1 >= '0') && (c1 <= '9'))
				b += ((c1 - '0') * 16);
			else if ((c1 >= 'a') && (c1 <= 'f'))
				b += ((c1 - 'a' + 10) * 16);
			else if ((c1 >= 'A') && (c1 <= 'F'))
				b += ((c1 - 'A' + 10) * 16);
			else
				throw new IllegalArgumentException("Bad hexadecimal digit");
			if ((c2 >= '0') && (c2 <= '9'))
				b += (c2 - '0');
			else if ((c2 >= 'a') && (c2 <= 'f'))
				b += (c2 - 'a' + 10);
			else if ((c2 >= 'A') && (c2 <= 'F'))
				b += (c2 - 'A' + 10);
			else
				throw new IllegalArgumentException("Bad hexadecimal digit");
			baos.write(b);
		}
		return (baos.toByteArray());

	}

	/**
	 * Convert a byte array into a printable format containing a
	 * String of hexadecimal digit characters (two per byte).
	 *
	 * @param bytes Byte array representation
	 */
	public static String convert(byte bytes[]) {

		StringBuffer sb = new StringBuffer(bytes.length * 2);
		for (int i = 0; i < bytes.length; i++) {
			sb.append(convertDigit((int) (bytes[i] >> 4)));
			sb.append(convertDigit((int) (bytes[i] & 0x0f)));
		}
		return (sb.toString());

	}

	/**
	 * [Private] Convert the specified value (0 .. 15) to the corresponding
	 * hexadecimal digit.
	 *
	 * @param value Value to be converted
	 */
	private static char convertDigit(int value) {

		value &= 0x0f;
		if (value >= 10)
			return ((char) (value - 10 + 'a'));
		else
			return ((char) (value + '0'));

	}

}
